I’m trying to use pin 25 on an Arduino Mega 2560 as a digital output, while also using pin A3 as an analog input. However, I’ve noticed that pin 25 is listed as ‘AD3’ on the pinout diagram. Does this mean it’s connected to pin A3, and would this cause interference if I was trying to use both these pins like this at once?
For these things, better to go to the schematic, I think.
Mega 2560 Schematic
Note that A3, the analog in, is on pin 94 of the chip, whereas pin AD3 is on pin 75 of the chip. Although I don't work with Mega's much, I'd say your okay.
No, pin 25 is bit #3 in input/output port A, which you would only use if you were directly accessing the input/output port registers in the atmega2560 processor. Analog pin A3 is bit #3 in input/output port K, likely KD3 if it is labeled on the pinout diagram you have (the notation differs between diagrams).
Right. This is one pin, what do you mean?
Analog input A3 maps to D57, not to D25.
No.
ATmega2560 can use external memory, AD3 is address/data line 3. Analog inputs are marked ADCn.